1. Katja Woth & Hans von Storch
Climate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)
Katja Woth & Hans von Storch
Institute for Coastal Research
GKSS Research Center
Geesthacht, Germany
Abstract Reference Number: 251
Abstract Title: Climate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)
Paper Number: A51F-01
Presentation Type: Oral
Presentation Date: Friday, 17 December
Location: 3016
Starting Time: 08:04
Time allotted: Time Allotted: 12 minutes
Climate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)
Hans von Storch & Katja Woth
Possible changes in North Sea storm surge climate are studied in a systematic manner.
Following up on previous studies, we use a tide-surge model to derive storm surge climate
and extremes from atmospheric conditions under present-day and enhanced greenhouse gas
conditions. Results for modeled storm surges obtained by using regional model output from
four RCMs, namely CLM (GKSS), RCAO (SMHI), REMO5 (MPI) and HIRHAM (DMI) are
presented.
The atmospheric regional simulations were prepared within the EU project PRUDENCE. The
research strategy of PRUDENCE is to compare simulations of different regional models
(RCMs) driven by the same global control and climate change simulations. These global
conditions, representative for and were prepared by the Hadley Center
based on the IPCC A2 SRES scenario. The effect on windiness of the enhanced greenhouse
gas conditions, projected by these four regional climate models was in all cases similar,
namely a moderate increase of high wind speeds in most parts of the North Sea during winter.
These simulated surface wind and pressure data have been used to run a storm surge model.
We show the expected storm-related changes in different storm surge parameters. For
instance, the largest increase of high water levels, defined as the 99.5%ile during winter
sampled every half hour would have to be expected along the southern and eastern North Sea
coast, with maximum values of around 30 cm, which is beyond the range of normal year-toyear
variations. Similar results can be found for all four experiments. Together with the
expected rise of mean water levels of 40 cm by IPCC (2001), the total increase is 70 cm at the
end of the 21st century under the assumptions of the rather severe A2 scenario. If an ECHAMscenario
A2 is used, quantitatively similar results are obtained, but in that case there are also
significant increases along parts of the UK coast.

2. Institute for Coastal Research GKSS, Germany
Assessing ongoing change of coastal climate.
Deriving scenarios of plausible, possible futures of coastal climates.
Special emphasis on wind-related aspects, i.e., wind force, storm surges and ocean waves.
Special emphasis on North Sea and Baltic Sea.
Participant in HIPOCAS, PRUDENCE and ENSEMBLES.

3. NCEP Globale Reanalysen ( 210 km x 210 km ) 1958 - 2002
BAW - TELEMAC 2D Wasserstand und barotrope Strömung UTC
REMO Windgeschwindigkeit und Richtung UTC
HIPOCAS: Für Rekonstruktionen verwendete Modellkette
Gebiet hier: Nordsee und östlicher Nordatlantik
WAM sig. Wellenhöhe und Richtung UTC
Rekonstruktionen am Beispiel einer neueren Arbeit, dem HIPOCAS Hindcast
Auflösung etwa 50 x 50 km
Auflösung zwischen etwa 100 m und 5km
Auflösung etwa 5 x 5 km

4. Climate risk assessments done with these models
Reconstruction of past and ongoing state and change
PCPnP futures (PCPnP = plausible, consistent, possible but not necessarily probable = scenarios)

5. Comparison of wind speed statistics with in-situ data: RCM is skillful in describing marine wind statistics
Not assimilated into NCEP (Ionic Sea)
These plots are the quantile-quantile diagrams (REMO & NCEP Vs Observations) for 10-m wind speed at 2 buoys station. The first one is an Atlantic offshore buoy (ZBGSO, located at
48.7N,12.40W), already assimilated by NCEP. The second one shows results from a Mediterranean buoy (ZATOS, located at 39.96N, 24.72E, Aegean Sea), whose data have NOT been previously assimilated by NCEP.

6. External Forcing – Future Scenarios
THE IPCC…scenarios corresponding to different storylines assume diff. Emission scenarios.
The main scenario characteristics are described in the Box. A2 assumes..…
B2 assumes… with ….and … producing therefore lower emissions and less future warming than A2
External Forcing – Future Scenarios

7. EU-Project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects)
GCM
RCMs
Regional Climate Models:
CLM - REMO - HIRHAM - RCAO
Global Climate Model (HadAM3) IPCC A2 SRES Scenario ( / )
today
today
Storm Surge Model for the North Sea:
- TRIM 3D
Impact
model
Impact scenarios
scenario
scenario
global
local
scale

8. A2 - CTL: changes in 99 % - iles of wind speed (6 hourly, DJF): west wind sector selected (247.5 to deg)
HIRHAM
RCAO
REMO5
CLM

9. Projections for the future / surge meteorological forcing: HIRHAM / RCA
Differences in inter-annual percentiles of surge / A2 - CTL: HIRHAM
Differences in inter-annual percentiles of surge / A2 - CTL: RCA

10. Mean change of winter 95%ile surge levels
Near coastal model cells

11. SREs emission scenarios: Impact on global sea level
According to scenario A2 and the specific set of GCM / RCMs, water level may rise in extreme situations by as much as
40 cm + 30 cm = 70 cm
along the German North Sea coast.
IPCC, 2001
SREs emission scenarios: Impact on global sea level

12. Conclusions
Dynamical models have been demonstrated to be a useful tool to describe the statistics, and changes thereof, of wind-related phenomena in coastal seas – wind force, storm surge, coastal currents and ocean waves.
An ensemble of regionalizations, derived from one global A2 scenario, results in rather similar changes of regional wind over the North sea and the associated change of surge levels.
Along the German North Sea coast, water levels may rise by up to 70 cm - of which 40 cm are due to mean sea level rise and 30 cm to different storm patterns.